The present invention generally relates to an electronic ballast, and more particularly to a circuit for regulating power in an electronic ballast.
Typically, an electronic ballast must regulate lamp power when operating a high-intensity discharge lamp. This is accomplished by sensing the lamp current and the lamp voltage either directly or indirectly and multiplying the two signals to get the wattage. The multiplication is usually done using microcontroller or a microprocessor. The wattage is then compared to the reference wattage. A feedback loop is provided in such a way that the error that results from this comparison is converted to a signal such that the lamp current is adjusted so that the measured lamp power is equal to the reference power.
However, such sensing circuitry can be expensive. In manufacturing electronics generally, any reduction in the necessary parts can be significant. In the field of electronic ballasts, any improvement which can reduce the cost of electronic control circuits is significant. For example, the reduction or elimination of detection circuitry can reduce part count and reduce cost significantly. Such cost reductions are particularly significant when a particular unit, such as an electronic ballast, is manufactured and sold in major quantities.
Accordingly, it is desirable to provide an improved electronic ballast in which the amount of sensing circuitry is reduced.
This disclosure describes a way in which an electronic ballast can operate a high intensity discharge (HID lamp) at a constant power without the need to sense the lamp current either directly or indirectly. Currently, all ballast manufacturers in the market provide power regulation by sensing both the voltage and current of the lamp either directly or indirectly. If there is no need to sense the lamp current then the circuitry associated with this sensing can be eliminated, resulting in a significant cost savings for the ballast.
The present invention relates to a circuit for regulating power in a high pressure discharge lamp that sets a current in the lamp based upon a detected voltage. According to another aspect of the invention, a method for regulating power in an electronic ballast of a high pressure discharge lamp comprises steps of detecting a voltage in the electronic ballast of the high pressure discharge lamp and setting a current in the electronic ballast based upon the detected voltage.
It is an object of the present invention to regulate power in an electronic ballast by controlling the current to a high intensity discharge lamp.
It is a further object of the present invention to eliminate the need for current sensing circuitry for lamp power regulation in an electronic ballast.
It is a further object of the present invention to set an appropriate current based upon the detected voltage in the high intensity discharge lamp.
It is a further object of the present invention to regulate the power in a high intensity discharge lamp by varying the current provided to a high intensity discharge lamp based upon the detected voltage.